1. Field of the Invention
The invention relates to a mass flowmeter of the Coriolis type, with a sensing tube that forms a single loop through which a medium flows during operation, and with excitation means for causing said loop to oscillate about an excitation axis of rotation during operation, said axis lying in the plane of said loop.
2. Description of the Related Art
Such a mass flowmeter is known from U.S. Pat. No. 4,658,657.
The known mass flowmeter comprises a looped tube that is not closed (half a turn) and that forms a transverse branch at one side which is connected to two lateral branches clamped in at the opposite side in a mounting beam. The latter is mounted in a support such that it can rotate about a central axis lying in the plane of the loop. An electromagnetic excitation system cooperating with the (magnetic) mounting beam provides an oscillatory rotation (vibration) of the mounting beam with the loop about the central axis. When a medium flows through the loop that rotates about the central axis, Coriolis forces are generated in the transverse branch that is oriented perpendicularly to the axis of rotation, resulting in a vibration of the loop about an axis perpendicular to the excitation axis of rotation. This vibration, which is proportional to the flow, is superimposed on the fundamental oscillation and leads to a phase shift between the oscillations performed by the ends of the transverse branch. The phase difference is proportional to the Coriolis force and accordingly to the flow.
It is a disadvantage of the known system, however, that the mounting beam used for the excitation of the loop constitutes an additional mass. This prevents a change in the excitation frequency as a function of the density of the medium flowing through the tube, with the result that a measurement of the density (an additional property of a Coriolis flowmeter) becomes less accurate.